The invention relates to an electronic ballast for stabilizing current in a gas discharge lamp.
The invention relates to an electronic ballast for stabilizing the current in a gas discharge lamp, comprising a holder with a wall, electronic components and at least one electroconductive element, which forms a connection between the individual electronic components and/or which can form a connection between the electronic components and the gas discharge lamp.
Such an electronic ballast is well known. A property of gas discharge lamps is that the electric resistance of these lamps is not constant, but decreases with increasing voltage. As a result, a slight increase of the voltage causes a disproportionately large increase of the current flowing through the lamp, which is undesirable. The ballast serves to limit and stabilize the current through the lamp. The ballast may also comprise a rectifier, which converts the AC voltage supplied by the power supply into a DC voltage, and a transformer which brings the voltage to the desired level.
In the known ballast, the electroconductive elements, which generally comprise connection wires and connectors, may be provided on a main printed circuit board (also referred to as printed wiring board or PCB) which is mounted in a metal or synthetic resin holder. As such a printed circuit board takes up extra space in the ballast, the connection wires are known to be alternatively provided on a foil which is attached to the holder, in which case the connectors are secured to the holder. The electronic components, which determine the electrical properties of the ballast, are provided on this printed circuit board or foil either directly or by means circuit cards. If the holder is made of metal, care should be taken that the electronic circuitry is properly insulated with respect to the holder, which is often achieved by using insulating foil.
There is a need for smaller-sized electronic ballasts, which are generally bar-shaped. Particularly the height of said ballasts is important as they must be fitted in a luminaire. It will be clear that a main printed circuit board takes up quite some space.
Another required quality of a ballast is a good dissipation of the heat generated by the electronic components. In this respect, a main printed circuit board, on which these components are placed, has an insulating effect and adversely affects an efficient heat dissipation. If the components are placed on a foil, which foil is secured directly onto the wall, this problem is less important, but there is a risk that the heat generated causes the foil to melt or to be damaged. Besides, the wiring on the foil is thin and vulnerable.
Therefore, it is an object of the invention to provide a compactly constructed electronic ballast, which demonstrates a satisfactory heat dissipation and is less sensitive to damage.
A further, important object of the invention is to reduce the number of production steps in the manufacture of an electronic ballast for a gas discharge lamp, thereby reducing the production costs. Another object is to reduce the number of components of such a ballast, thereby further reducing the risk of defects.
To achieve this, at least a part of the conductive element which extends parallel to the wall is enclosed in the material of said wall. As a result thereof, the wall takes over at least a part of the functions of the main printed circuit board, thereby rendering said main printed circuit board at least partly redundant. By virtue thereof, the ballast can be more compactly constructed, or the space available for the electronic components on the main printed circuit board is increased, which is favorable for the electrical insulation between the components. It also leads to a reduction of the number of production steps and the number of components. Since the electronic components can be mounted on the holder, either directly or by means of printed circuit boards, the heat dissipation is improved too.
Preferably, the material of the wall comprises a synthetic resin, and, preferably, the holder is manufactured by means of injection molding, the conductive element being enclosed in the wall in the injection molding process. By virtue of such a method, the conductive elements no longer have to be separately provided, as is the case when the conductive elements are situated on a printed circuit board or a foil, so that said method saves both time and costs.
The electroconductive element further preferably comprises at least one connector by means of which said electroconductive wire and/or an electronic component can be connected with the electroconductive element. Advantageously, the connection wires and the connectors are manufactured from a single piece of metal, resulting in a sturdy construction and, at the same time, a further reduction of the number of components, thereby increasing the reliability.
The connector preferably comprises an elastically deformable clamping portion, which presses against the holder, whereby an electroconductive wire can be clamped between the clamping portion and the holder. More preferably, the clamping portion presses against the holder at an angle, with the angle included by the clamping portion and the holder, at the side where the electroconductive wire to be clamped may run, being an acute angle. The connection wires for connecting the gas discharge lamp can be readily inserted into these connectors, the clamping portion automatically being slightly lifted during said insertion operation. If a pulling force is subsequently exerted on the wire, the wire becomes clamped between the clamping portion and the holder.
Preferably, the ballast further comprises at least one plate-shaped cooling element, which is provided in or on the wall in which the electroconductive element is enclosed. As the cooling element is grounded, it more preferably also serves as an electromagnetic shield. This cooling element, which can be provided in the wall at the same time as the electroconductive elements, increase the heat-dissipation capacity and also cause the high-frequency electromagnetic interference to be reduced.
The ballast also preferably comprises a printed circuit board with electronic components, said printed circuit board extending substantially perpendicularly with respect to the wall in which the electroconductive element is enclosed. In this manner, electroconductive elements, which in turn are perpendicularly placed on this printed circuit board, can be brought into heat-conducting contact, at the location of a part of said electroconductive elements which is subject to a substantial increase in temperature during operation, with the wall which is preferably provided with cooling elements. If necessary, a heat-conducting casting mass may be provided between the components and the wall.
Preferably, the holder comprises a bottom plate, which forms the wall wherein the electroconductive element is enclosed, and a cover which is connected with said bottom plate. This enables the electronic circuitry to be readily placed in the holder, after which the cover is mounted.
Preferably, a plurality of electroconductive elements are punched from a plate of metal before they are enclosed in the wall. More preferably, at least one cooling element is simultaneously punched from said plate of metal, which cooling element is provided in or on the wall. This method of manufacturing these elements is very efficient and inexpensive.
Preferably, connectors are formed at the electroconductive element and/or the cooling element by bending parts of the punched plate portions. The connector preferably extends substantially perpendicularly from the electroconductive element. Also this method enables connectors to be manufactured very efficiently and inexpensively.
Preferably, the electroconductive elements and/or the cooling elements are fixed substantially with respect to one another between the time that they are punched and the time that they are enclosed in and/or provided on the wall. The manufacture of the components, the formation of the connectors and the enclosure in the wall are carried out in a single continuous process step, which is very efficient and cost-saving.
The invention also relates to a luminaire for a gas discharge lamp, comprising a lamp holder, connectors for connecting a gas discharge lamp and an electronic ballast as claimed in any one of the preceding claims, which ballast is connected to at least one of the connectors.
The invention further relates to a method of manufacturing an electronic ballast for stabilizing the current in a gas discharge lamp, wherein electronic components and at least one electroconductive element are placed in a holder with a wall so as to make sure that this electroconductive element forms a connection between the individual electronic components and/or is capable of forming a connection between the electronic components and the gas discharge lamp, at least a part of the electroconductive element which extends parallel to the wall being enclosed in the material of said wall.
These and other objects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.